1. Field of the Invention
This invention relates generally to data communication system and more particulary to a digital apparatus and method for a data bit operated squelch.
2. Description of the Prior Art
Phase shift keyed (PSK) modulation techniques are widely used in digital signalling over RF communication channels. In digital phase shift keying, digital information is communicated over the channel by sequentially transmitting carrier pulses of constant amplitude, angular frequency and duration but of different relative phase. Demodulation of PSK signals is accomplished by detecting the relative phase of the incoming signal and using the phase information obtained to determine the data content of the modulated signal. Present PSK demodulator systems generally employ hybrid, arrangements of digital and analogue circuit components. Such PSK demodulators generally require on-site calibration and periodic readjustment.
Many of these problems can be solved by utilizing a sample based phase locked loop demodulation and detection method. With such system it is often desirable to provide squelch capability based upon bit detection and with rapid response. Prior art circuits for bit detection required complex circuitry with fixed parameters and were unduly expensive to manufacture.